Elevators having two elevator cars placed one above the other in the same car frame are used e.g. in tall buildings to increase the transport capacity. Such double-deck elevators can serve e.g. as collector elevators.
Traditionally, double-deck elevators have fixed inter-car distances, as described e.g. in the old German patent specification DE1113293. However, double-deck elevators with a fixed inter-car distance involve the problem that in many buildings the distances between floors are not equal. Often, especially in modern tall buildings, the entrance lobby is higher than the other stories. Likewise, the building may have other special stories of varying height. In addition, in tall buildings the tolerances may repeat themselves, and thus the story heights of upper and lower floors may be different. In such buildings, in double-deck elevator solutions with a fixed inter-car distance only one of the cars can be driven exactly to the correct position while the other one remains above or below the floor level by a distance corresponding to the difference.
To solve the above-mentioned problem, double-deck elevators have been developed in which the vertical distance between the elevator cars mounted in the same car frame, i.e. the inter-floor distance can be adjusted. European patent application No. EP1074503 proposes a number of solutions to address the above-mentioned problem. FIG. 1 of the aforesaid publication illustrates a solution wherein the elevator cars in the car frame are raised or lowered in relation to each other and the car frame by means of a motor or equivalent provided in the car frame.
Similarly, FIG. 2 illustrates another prior-art solution, which corresponds to e.g. U.S. Pat. No. 5,907,136. In this known solution, the elevator cars in the car frame are raised or lowered in relation to each other and the car frame by means of a jack and a scissors mechanism provided in the car frame. In addition, the car frame comprises an intermediate beam, which carries the fixing point of the joint of the scissors mechanism. The upper car is raised by means of a hoisting device provided in the car frame, such as a motor or by rotating lifting screws or by means of power cylinders. When the upper car is moving in one direction, the lower car, driven by the scissors mechanism, is simultaneously moving in the other direction.
The aforesaid EP specification EP1074503 itself proposes two elevator cars placed one above the other in the car frame and coupled to be moved by thick screw bars in relation to each other and the car frame. The screw bar moving the upper car and the screw bar moving the lower car have threads of opposite pitch, and consequently the elevator cars move in opposite directions when the screw bars are rotated. The drive motor of the screw bars is placed in the upper part of the car frame.
Although the prior-art solutions referred to above do overcome the aforesaid drawback caused by a fixed inter-car distance in double-deck elevators, these solutions are not without problems. All the above-mentioned solutions are complicated in structure and involve unnecessary additional weight in the car frame. Moreover, they take up space that would be needed for other equipment in the car frame. A further problem is that the drive means, such as motors and power cylinders in the car frame require operating energy, which has to be supplied to the moving car frame from outside. For example, an electric motor requires separate supply of power via the car cable to the car frame. Likewise, the power cylinders or equivalent need their own power supply. An additional problem is that the devices moving with the car frame are difficult to adjust and maintain because these operations have to be performed in the elevator shaft on the top of the car frame or otherwise in connection with the car frame.